Organic Chemistry Final Exam Review Dr Hilinski Constitutional isomers the same molecular formula but the atoms are arranged differently Resonance Structures the same molecular formula but the electrons are arranged differently To draw a Lewis Structure you need to add up the number of valence electrons for each atom in the molecule then draw out the structure and disperse the electrons so that each atom satisfies the octet rule Drawing Hybrid Structures of resonance Double bonds should have one solid line and one dashed line Do not show electrons on any atoms Calculate the average formal charge for each atom by looking at the charge of the same atom in all structures and then dividing it by the total amount of structures Calculate bond order by choosing a bond and counting how many bonds there are in each structure then dividing by the total amount of structures Bond orderC O 3 2 Bond orderC H 1 Oxidation loosing electrons loosing H Oxygen contest increases Reduction Gaining electrons gaining H Oxygen or bonds to it decrease The more important resonance structure The negative charge is on the more electronegative atom The structure that has the least separation of charges The structure with the most double bonds Ionic bond when 2 oppositely charges ions bond Na Cl cid 224 NaCl Covalent bond when 2 atoms share electrons H H cid 224 H H Nonpolar molecules do not have a dipole moment but polar molecules do The dipole moment goes towards the most electronegative atom in the molecule SO2 is More polar than CO2 because of its positive charge and uneven distribution of electrons Formula H Name Hydrogen ion proton H H H H Acids Bases Equilibrium lies towards the weaker acid Lewis Acid an electron pair acceptor positively charged Lewis Base an electron pair donor negatively charged Hydrogen atom Hydrogen ion Hydrogen molecule H2 As you go down a column in the periodic table acidity increases because the molecule becomes larger making it easier for a proton to dissociate The lower the pKa is the more acidic it is The more resonance structures something has the more stable it is The left structure is geminally distributed and the right structure is vicinally distributed BASIC NAMING with yl ane When naming an alkyl group replace Memorize isopropyl isobutyl sec butyl tert butyl neopentane there is a document in the course library with them all listed Primary Carbon a carbon that is bonded to 1 other carbons Secondary Carbon a carbon that is bonded to 2 other carbons Tertiary Carbon a carbon that is bonded to 3 other carbons Physical Properties Alkanes and cycloalkanes are nonpolar and insoluble in water The boiling point of alkanes increases as the number of carbons increases Branched alkanes have lower boiling points than unbranched because they are more stable The more stable an alkane the lower the heat of combustion is Oxidation Reduction To calculate the average oxidation you have to use what you already know O 2 H 1 N 3 in NH2 X 1 x OH Br Cl F I Addition elimination reactions taking or adding water to a molecule have no effect on the oxidation level Carbon in its most oxidized form CO2 Carbon in its most reduced form CH4 Sp3 hybridization allows for carbon to bind to 4 other substituents Sp3 has 0 pi bonds no double bonds Sp2 has 1 pi bond a double bond Sp has 2 pi bonds has a triple bond Pi orbitals are parallel and they don t hold molecules together they can make bonds stronger though Single bonds are ALWAYs sigma bonds there can only be one sigma bond between atoms the rest are pi bonds Liquid nitrogen is diamagnetic repelled in a magnetic field and O2 is paramagnetic Strain and Confirmations Different Configuration break bonds and reform them rotations about a single bond Staggered minimum in energy Anti 180 degrees between two main groups most stable lowest in energy Gauche 60 degrees stability depends on what is interacting Eclipsed high in energy atoms are on top of each other A potential energy diagram is a graph of increasing potential energy vs torsional angel in degrees Angle strain strain a molecule has because one or more of its bond angles deviates from the ideal angle 109 5 Torsional strain destabilization that results when bonds on adjacent atoms are NOT staggered Van der Waals strain destabilization that results when atoms or groups on nonadjacent atoms are too close to one another Cyclopropane has angle strain and torsional strain because the C H bonds are all eclipsed Cyclobutane relieves this strain by adopting a puckered form The puckering decreases eclipsing interactions Cyclopentane has small angle strain but the torsional strain is substantial because of the eclipsing hydrogen s in its planar form It relieves this strain by forming an envelope or half chair confirmation Cyclohexane is free of angle and torsional strain because of its chair confirmation A less stable form is the boat and less then the boat is the skew boat The boats are all above the chair still Torsional strain Methyl Primary Secondary Tertiary The most stable form of a chair will have the most strenuous alkyl group as equatorial 1 4 substituted and 1 2 substituted cyclohexanes are more stable in the trans position 1 3 substituted chairs are more stable when they are cis 1 3 diaxial strain results in a less stable confirmation When drawing chairs allow axial bonds to alternate starting up from the head of the chair and down from the foot of the chair leave space in the back line of the chair for up axial bonds that come up front Stereoisomers isomers that have their atoms bonded in the same order and have the same constitution but differ in the arrangements of atoms in space usually cis vs trans Naming Spiro compounds Start numbering from smallest ring to largest Don t start numbering at the Spiro carbon Take the path that has the substituent at the lowest locant Place numbers from smallest to largest after the spiro prefix Bicyclic compounds Start counting at either bridge head and start numbering towards largest bridge giving substituents the lowest locant number It must ALWAYS have 3 number in brackets even if there is not bridge just put a 0 Anti pointing away from lowest number bridge Syn pointing towards lowest number bridge Endo pointing away from highest number bridge Exo pointing towards highest number bridge Halides go in alphabetical order and give them the lowest umber Alkyl Halides Functional class the alkyl group and halide are separate words Starts counting the chain at the